1. Field of the Invention
This invention relates to a sheet material separating device for separating sheet materials, cut sheet materials (leaf materials) such as transfer materials, photosensitive paper sheets, electrostatic recording paper sheets and printing paper sheets) set on a paper supply portion, for example, in a printer or a copying apparatus one by one and conveying them to a processing portion such as an image forming portion.
More particularly, the present invention relates to a sheet material separating device of a construction which has a sheet material conveying member for conveying sheet materials in a predetermined direction and a sheet material separating member urged against the surface of said sheet material conveying member with a predetermined pressure force and in which of two or more sheet materials whose leading end portions have entered between said two members due to the cooperation between said two members, the sheet material which is in direct contact with the sheet material conveying member is conveyed between the contact portions of the two members by the conveying force of the sheet material conveying member and the passage of the other sheet materials is discharged by the sheet material separating member, whereby the sheet materials are separated and conveyed one by one.
2. Related Background Art
FIG. 8 of the accompanying drawings shows an example of the conventional sheet material separating device of the construction as described above
In FIG. 8, the reference numeral 1 designates a paper feeding and separating roller (hereinafter referred to as the "paper feeding roller") as a sheet material conveying member rotatively driven about a shaft 1a in a clockwise direction indicated by arrow. This paper feeding roller 1 is a cut-away circular roller of D-shaped cross-section, and during non-feeding of paper, it stands by with its cut-away planar portion 1b facing downward, and is intermittently driven for one full rotation by each paper feeding signal. The reference numeral 2 denotes an auxiliary roller supported coaxially with the paper feeding roller 1. This auxiliary roller 2 has a diameter slightly smaller than the diameter of the paper feeding roller 1 and is freely rotatable relative to the shaft 1a.
The reference numeral 4 designates a separating unit as a sheet material separating member. The separating unit 4 comprises a friction member 3 adhesively secured to a pedestal 4a, and is fixedly held on the upper surface of the inwardly extending fore end portion of a paper feed guide plate 5 having its fore end portion inwardly extending to below the paper feeding roller 1. The guide plate 5 is supported for pivotal movement about a pivot shaft 5a, and is normally rotatively biased in a raising direction (a counter-clockwise direction) by a pull-up spring 6. By this rotative biasing force, the friction member 3 of the separating unit 4 is kept in pressure contact with the lower surface portion of the paper feeding roller 1 or the lower surface portion of the auxiliary roller 2 with a predetermined pressure force.
The reference numeral 7 denotes a sheet material cassette (only the fore end portion of which is shown) mounted on a cassette receptacle (not shown) below the paper feeding roller 1. The reference character 7a designates a cassette box, the reference character 7b denotes a cassette intermediate plate having its fore end portion normally upwardly biased by a spring 7c, and the letter P designates sheet materials supported on the cassette intermediate plate 7b and contained in the cassette box 7a. In the mounted condition of the cassette 7, the leading ends of the supported sheet materials P are positioned below the paper feeding roller 1, and the upper surface of the leading end portion of the uppermost one of the supported sheet materials P is kept in pressure contact with the lower surface portion of the paper feeding roller 1 or the lower surface portion of the auxiliary roller 2 by the upward biasing force of the spring 7c with a predetermined pressure force.
One full rotation intermittent driving of the paper feeding roller 1 in the clockwise direction is effected by a paper feeding signal and the peripheral surface 1c of the paper feeding roller 1 comes into contact with the upper surface of the leading end portion of the uppermost one of the supported sheet materials P, whereby a paying-away force acts on the uppermost sheet material, which is thus fed out of the cassette 7 to between the paper feeding roller 1 and the friction member 3 which is in pressure contact with the surface of the roller 1. The uppermost sheet material thus fed out is conveyed between the contact portions of the paper feeding roller 1 and the friction member 3 by the rotational force of the paper feeding roller 1.
As the uppermost sheet material is paid away or conveyed by the continued paper feeding, the next sheet material and so forth are dragged due to the frictional force therebetween and by the movement of the uppermost sheet material and are gradually moved forward out of the cassette 7. Thus, as shown in FIG. 9A of the accompanying drawings, the leading end portions of the sheet materials heapingly come into a wedge-shaped space M formed by the paper feeding roller 1 and the friction member 3 upstream with respect to the direction of conveyance of the sheet materials. However, even in such a state, only the uppermost sheet material that is in direct contact with the paper feeding roller 1 is handled by the rotational force of the paper feeding roller 1 and passes between the contact portions of the paper feeding roller 1 and the friction member 3, and the next sheet materials and so forth are precluded from moving forward by the frictional force of the friction member 3 and do not move forwardly of the contact portions of the paper feeding roller 1 and the friction member 3.
That is, only the uppermost one of the supported sheet materials P passes between the paper feeding roller 1 and the friction member 3 without causing the trouble of double feeding with respect to the next sheet material and so forth and thus, the sheet materials are separated one by one and conveyed to a sheet material processing portion such as an image forming portion through a sheet path formed by guide plates 5, 5A and 5B.
The paper feeding roller 1, when driven for one full rotation, is stopped from rotating in a rotational angle state in which the cut-away planar portion thereof faces downward, but until then, the leading end portion of the uppermost sheet material conveyed by the paper feeding roller 1 toward the sheet material processing portion through the sheet path formed by the guide plates 5, 5A and 5B is nipped between a pair of relay conveying rollers (not shown), and thereafter the conveyance of the sheet material is continuedly done by the conveying force of the pair of relay conveying rollers. The trailing end portion of the sheet material passes in a pulling-out fashion between the auxiliary roller 2 and the friction member 3 while rotating the auxiliary roller 2 about the shaft 1a.
The auxiliary roller 2 serves to keep the paper feeding roller 1 apart from the friction member 3 so as not to contact with the sheet materials P when during non-feeding, the paper feeding roller 1 is being stopped from rotating in the rotational angle state in which the cut-away planar portion faces downward.
Even if as described previously in connection with FIG. 9A, the leading end portions of a plurality of sheet materials heapingly come into the wedge-shaped space M formed by the paper feeding roller 1 and the friction member 3, the direct contact between the paper feeding roller 1 and the friction member 3 is kept in almost all cases until the uppermost sheet material which is in direct contact with the paper feeding roller 1 wedges into the contact portions of the roller 1 and the member 3. Also, when the friction resistance between the paper feeding roller 1 and the sheet material P is C and the friction resistance between the friction member 3 and the sheet material P is D and the friction resistance between the adjacent sheet materials P is E, these three friction resistances are kept in the relation that C&gt;D&gt;E, and the performance of separating the sheet materials one by one is not reduced.
However, where sheet materials of high mutual friction resistance are used as the sheet materials P, the force with which the leading end portions of the plurality of sheet materials wedge into the aforementioned wedge-shaped space becomes strong. In that case, said wedging force overcomes the pressure contact force by the spring 6 of the separating unit 4 against the paper feeding roller 1, and the separating unit 4 is pushed down away from the surface of the paper feeding roller 1 against the force of the spring 6. Thus, the amount of wedging of the leading end portions of the plurality of sheet materials into the wedge-shaped space M becomes excessively great, and as shown in FIG. 9B of the accompanying drawings, the friction member 3 of the separating unit 4 separates from the surface of the paper feeding roller 1 to thereby create a gap .delta. therebetween.
When such a gap .delta. is created, the force with which the sheet materials (the second and subsequent sheet materials) underlying the uppermost sheet material (the first sheet material) directly contacted by the paper feeding roller 1 is urged against the friction member 3 is reduced or disappears downstream of the friction member 3 with respect to the direction of conveyance of the sheet materials. Therefore, the separated state of the friction member 3 from the sheet materials is deteriorated and thus, the second and subsequent sheet materials are fed past and between the paper feeding roller 1 and the friction member 3 with the first sheet material. That is, the trouble of double feeding of the sheet materials is caused.
The problem as noted above arises even in the sheet separating device as disclosed in U.S. Pat. No. 4,032,135 which has a paper feeding roller discretely from a roller cooperating with a friction member to effect separation of sheets.